1. Field of the Invention
The present invention relates generally to downhole tools for use in wells, and more particularly, but not by way of limitation, to improvements in a downhole tester valve.
2. Description of the Prior Art
During the course of drilling an oil well, one operation which is often performed is to lower a testing string into the well to test the production capabilities of the hydrocarbon producing underground formations intersected by the well. This testing is accomplished by lowering a string of pipe, commonly referred to as a drill pipe, into the well with the formation tester valve attached to the lower end of the string of pipe and oriented in a closed position, and with a packer attached below the formation tester valve. This string of the pipe with the attached testing equipment is generally referred to as a well test string. The basic components of a typical well test string are seen for example in FIG. 1 of U.S. Pat. No. 4,295,361 to McMahan, the details of which are incorporated herein by reference.
Once the test string is lowered to the desired final position, the packer means is set to seal off the annulus between the test string and the well casing, and the formation tester valve is opened to allow the underground formation to produce through the test string.
One example of such a tester valve is that shown in U.S. Pat. Nos. 4,579,174; 4,582,140; and 4,624,317, all to Barrington and all assigned to the assignee of the present invention.
The operation of these tools involves a telescoping action between two portions of the tool which serves to open the tester valve when weight is set down on the tool after the packer has been set in the well below the tool. This telescoping action occurs relatively slowly due to a hydraulic time delay built into the tool. The purpose of this time delay is to allow the formation tester valve to transmit compressional hydraulic forces for relatively short periods of time without actuating the valve, and to transmit weight through its hydraulic impedance system to apply drill pipe weight to the packer below. This is necessary for a number of reasons. For example, when the well test string is being run into the well bore, the test string often encounters obstructions in the well bore and weight must be set down on the test string for a short period of time in order to push the test string past these obstructions. Also, once the test string is in its desired location, various tools located below the formation tester valve, such as for example the packer, often are designed to be set by lowering drill pipe weight on the test string. The packer must seal against the well bore before the tester valve opens, and this is assured by the time delay built into the telescoping action of the tool.
Thus, it has been found desirable to provide such formation tester valves with a hydraulic time delay device which requires that sufficient weight be set down on the formation tester valve for a sufficient period of time, on the order of several minutes, before the formation tester valve will actually open.
Also, the hydraulic time delay device has been constructed so that the final portion of telescoping motion will occur very rapidly thus jiggling the drill pipe at the surface and providing a positive indication to personnel operating the well that the tester valve is open to begin the flow test of the hydrocarbon producing zone of the well.